An experimental test of the relationship between seed size and competitive ability in annual plants

Competition–colonization tradeoff models explain the coexistence of competing species in terms of a tradeoff between competitive ability and colonization ability. One class of such models is based on the idea that seed size determines competitive ability, seed number determines colonization ability, and the two traits are negatively correlated such that higher competitive ability of large‐seeded species compensates for their smaller seed number. According to such models, species inhabiting the same community should show a distinct ranking of competitive ability and this ranking should be correlated with seed size. We tested these predictions using a greenhouse competition experiment focusing on 25 annual species that coexist in sandy habitats of the Mediterranean region in Israel. Rankings of species based on their competitive effects on two independent phytometers were positively correlated. Corresponding rankings based on competitive responses were also correlated. Rankings based on competitive effects were correlated with those based on competitive responses. Yet, in spite of the clear hierarchy in all measures of competitive ability, none of the measures was correlated with seed size. While lack of correlation between seed size and competitive ability has been documented in some systems, our study is the first time that absence of such correlation is documented in a system where the existence of competition is well established and the component species show a clear hierarchy of competitive ability.     

Respiratory oscillator entrainment by periodic vagal afferentes: An experimental test of a model

This communication compares the well known phenomenon of respiratory driving by the respiratory pump through the Breuer Hering reflex with a model (Segundo, 1979) of a neuronal pacemaker (i.e. regularly firing) interactions via IPSP's. The assumption involves a linear dependence (“delay function”) of the postsynaptic interval lengthening (or “delay”) produced by the IPSP's on the position (or “phase”) with respect to the preceding spike of the latter's arrival. Cats anesthetized and paralized with gallamine were artificially ventilated using a computer driven respirator. The pump period and the respiratory period (identified by the phrenic discharge) corresponded to the model's presynaptic pacemaker interval and to that of the post synaptic one, respectively. The delay of the respiratory period by an inflation was related linearly and in increasing manner to the latter's phase with respect to the inspiration onset. In the steady state, plots of average respiratory period versus pump period consisted in a succession of broad “paradoxical” segments with positive slopes 3, 2, 1, 1/2, 1/3 in which respiration was locked with the pump as predicted by the model. The locked condition were less easy to reach when F_{A CO 2}increased or when level of anaesthesia decreased. The limits of paradoxical segments were different when measured using pump periods that increased or using periods that decreased. There was therefore a hysteresis as if the delay function parameters changed, a behavior that was not part of the model that assumed fixed characteristics. These modifications were related to dependency of each cycle on the preceding one. The model proposed for simple neuronal pacemaker interactions can thus be applied satisfactorily to the drive of the complex respiratory neuronal oscillator by the respiratory pump through Breuer Hering reflex, providing nevertheless some additonal assumptions concerning respiratory cycle interdependency are introduced to account for the hysteresis phenomenon. The Breuer Hering reflex could be considered as the equivalent of IPSP acting on the central respiratory oscillator. F_{A CO 2}increase and anesthesia level decrease produced the same effect as the addition of noise to the model's presynaptic pacemaker, thus leading to the hypothesis that they act by adding noise (e.g., randomly distributed excitatory input) at the level of Breuer Hering reflex inhibition.     

An experimental test of colonization ability in the potentially invasive Didemnum perlucidum (Tunicata, Ascidiacea)

Exotic species invasions are one of the greatest threats to marine systems and ascidians have many characteristics that favor transport, colonization and establishment into new regions. Didemnum perlucidum is a widespread species that has been introduced into tropical ports around the world. Here we examine the colonizing ability of D. perlucidum by experimental use of artificial plates in a shellfish culture. The experiment comprised paired plates for colonization (bare and occupied) in 16 monthly replicates. Recruitment and space occupation were compared between bare and occupied plates and an estimation of reproductive effort was based on the number of larvae produced in each of ten colonies collected on the culture structures. D. perlucidum reproduced continuously but greatest reproduction occurred between December 2006 and May 2007. While recruitment was somewhat greater (number of new colonies) on bare plates, this species can colonize already occupied substrates and, surprisingly, colony area was always similar between treatments. Thus, while fewer colonies formed on occupied plates, once formed, colonies grew at rates similar to those on clean plates. Thus, D. perlucidum colonizes substrates very efficiently, especially when unoccupied space is available.     

An experimental test of frequency-dependent food selection: winter browsing by moose

Penned moose Alces alces (L.) offered birch and rowan trees in various proportions in experimental tests showed a clear preference for birch both in terms of selection and use of trees. Both tree selection and tree use was frequency-independent, i.e. the preference for birches did not vary with either the number of birches, or total birch biomass available. The preference for birch was not absolute, i.e. rowans were also present in the diet. Birch were more profitable than rowans in terms of biomass intake rate, whereas rowans were more "nutritious" than birches. The results are consistent with both the optimal diet theory and the "nutrient mixture" hypothesis, although neither of the hypotheses are unambiguous regarding frequency-dependent food selection. It is argued, however, that tree selection and use by moose rather should be considered as a patch use problem and that trees should not be regarded as particulate food items as in most foraging models.     

The HKA test revisited: a maximum-likelihood-ratio test of the standard neutral model

We present a maximum-likelihood-ratio test of the standard neutral model, using multilocus data on polymorphism within species and divergence between species. The model is based on the Hudson-Kreitman-Aguade (HKA) test, but allows for an explicit test of selection at individual loci in a multilocus framework. We use coalescent simulations to show that the likelihood-ratio test statistic is conservative, particularly when the assumption of no recombination is violated. Application of the method to polymorphism data from 18 loci from a population of Arabidopsis lyrata provides significant evidence for a balanced polymorphism at a candidate locus thought to be linked to the centromere. The method is also applied to polymorphism data in maize, providing support for the hypothesis of directional selection on genes in the starch pathway.     

An experimental test of limits to tree establishment in Arctic tundra

1 Five treeline species had low seed germination rates and low survivorship and growth of seedlings when transplanted into Alaskan tundra. Seed germination of all species increased with experimental warming, suggesting that the present treeline may in part result from unsuccessful recruitment under cold conditions.
2 Growth, biomass and survivorship of seedlings of treeline species transplanted into tundra were largely unaffected by experimental warming. However, transplanted seedlings of three species ( Betula papyrifera , Picea glauca and Populus tremuloides ) grew more when below‐ground competition with the extant community was reduced. All three measures of transplant performance were greater in shrub tundra than in the less productive tussock or heath tundra. Establishment of trees in tundra may thus be prevented by low resource availability and competition.
3 Two species ( Alnus crispa and Populus balsamifera ) had low seed germination and survivorship of germinated seeds; transplants of these species did not respond to the manipulations and lost biomass following transplanting into tundra. Isolated populations of these two species north of the present treeline in arctic Alaska probably became established during mid‐Holocene warming rather than in recent times.
4 Of all the species studied here, Picea glauca was the most likely to invade intact upland tundra. Its seeds had the highest germination rates and it was the only species whose seedlings survived subsequently. Furthermore, transplanted seedlings of Picea glauca had relatively high survivorship and positive growth in tundra, especially in treatments that increased air temperature or nutrient availability, two factors likely to increase with climate warming.     

Non-Invasive monitoring of diaphragmatic timing by means of surface contact sensors: An experimental study in dogs

Background

The predictive role of many cytokines has not been well defined in Acute Respiratory Distress Syndrome (ARDS).

Methods

We measured prospectively IL-4, IL-6, IL-6 receptor, IL-8, and IL-10, in the serum and bronchoalveolar lavage fluid (BALF) in 59 patients who were admitted to ICU in order to identify predictive factors for the course and outcome of ARDS. The patients were divided into three groups: those fulfilling the criteria for ARDS (n = 20, group A), those at risk for ARDS and developed ARDS within 48 hours (n = 12, group B), and those at risk for ARDS but never developed ARDS (n = 27, group C).

Results

An excellent negative predictive value for ARDS development was found for IL-6 in BALF and serum (100% and 95%, respectively). IL-8 in BALF and IL-8 and IL-10 serum levels were higher in non-survivors in all studied groups, and were associated with a high negative predictive value. A significant correlation was found between IL-8 and APACHE score (r = 0.60, p < 0.0001). Similarly, IL-6 and IL-6r were highly correlated with PaO2/FiO2 (r = -0.27, p < 0.05 and r = -0.55, p < 0.0001, respectively).

Conclusions

BALF and serum levels of the studied cytokines on admission may provide valuable information for ARDS development in patients at risk, and outcome in patients either in ARDS or in at risk for ARDS.     

Assessing the diagnostic validity of a structured psychiatric interview in a first-admission hospital sample

The use of structured psychiatric interviews performed by non-cliniciansis frequent for research purposes and is becoming increasingly common in clini-calpractice. The validity of such interviews has rarely been evaluated empirically.In this study of a sample of 100 diagnostically heterogeneous, first-admittedinpatients, the results of an assessment with the Structured Clinical Interviewfor DSM-IV (SCID), yielding a DSM-IV diagnosis and performed by a trainednon-clinician, were compared with a consensus lifetime best diagnostic estimate(DSM-IV) by two experienced research clinicians, based on multiple sourcesof information, which included videotaped comprehensive semi-structured narrativeinterviews. The overall kappa agreement was 0.18. The sensitivity and specificityfor the diagnosis of schizophrenia by SCID were 19% and 100%, respectively.It is concluded that structured interviews performed by non-clinicians arenot recommendable for clinical work and should only be used in research withcertain precautions. It is suggested that a revival of systematic theoreticaland practical training in psychopathology is an obvious way forward in orderto improve the validity and therapeutic utility of psychiatric diagnosis.     

Competitive resource sharing: An experimental test of a learning rule for ESSs

Six sticklebacks (Gasterosteus aculeatus) distributed themselves between two simulated drift food patches in the ratio of patch profitabilities (Milinski 1979). The present study investigated the rule with which each fish decides to stay in one or the other patch, and whether the fish have more difficulties in reaching a decision when the prey is supplied irregularly as is the case under natural conditions. With frame by frame analysis of filmed experiments the hunting success and sampling effort of each individual fish could be determined continuously. The results support the hypothesis that the fish used the relative payoff sum (RPS) learning rule (Harley 1981; Regelmann 1984). There was a close correlation between all decisions of individual fish during a trial, whether to stay or leave a patch, and decisions predicted by the RPS learning rule using the actual experience of the fish. Differences in competitive ability between the fish influenced the dynamics of the distribution in the predicted way, the more successful competitors deciding earlier where to stay than the less successful ones. This had the effect that the good competitors as well as the poor ones were distributed between the patches in the ratio of patch profitabilities. It is also compatible with the RPS learning rule that the fish reached their decision as quickly whether they were supplied with prey regularly or irregularly.     

An approach to the critical assessment of the experimental conditions in practical molecular biology:: isolation of plant DNA

A plant molecular biology laboratory class experiment, based on real lab situations, is proposed to illustrate to the students how the assessment of the experimental conditions and the correct application of the technical details are critical also with an established procedure. During plant genomic DNA isolation and purification, a number of undesired effects, including DNA shearing and formation of secondary compounds, may take place. To simulate such events, we have set up a simple practical laboratory experiment in which the students are asked to isolate plant DNA under three different working conditions, from an optimal to a coarse one. The subsequent analyses on the extracted DNA enable the students to evaluate the influence of these different manipulations on DNA yield and quality. The experiment described can help the students to adopt a critical approach when interpreting the results of common preparative molecular techniques.     

Isometric back muscle endurance: An EMG study on the criterion validity of the Ito test

The validity of the Sorensen test as a measure for back muscle endurance is controversial due to a possible impact of hip extensor muscles. The aim of this study was to investigate the criterion validity of an alternative test (Ito test) compared to the Sorensen test. Both procedures were performed by 29 healthy subjects (11 women) for 5 s and until exhaustion (randomized order). EMG activity was measured from 3 lumbar back and 3 hip extensor muscles. Muscular involvement in test positions was calculated as percentage of maximal voluntary contraction (MVC). Muscle fatigue was determined by the normalized regression coefficient of the median frequencies of the EMG power spectrum (NMF_slope). Prediction of holding time by NMF_slope values was investigated using regression analysis. In the test positions, the hamstring muscles were activated to a higher MVC percentage in the Sorensen than in the Ito test, while the iliocostalis muscle was less activated. Similarly, the iliocostalis (p = 0.006) and the multifidi muscles (p = 0.03) significantly contributed to predict holding time in the Ito test, whereas the multifidi muscles (p = 0.001) and the semitendinosus muscle (p = 0.046) did so in the Sorensen test. The results of this study indicate that the Ito test might present a valuable alternative for testing back muscle endurance in LBP patients.     

An experimental test of the testosterone mediated oxidation handicap hypothesis in a wild bird

The oxidation handicap hypothesis (OHH) proposed that honesty in sexual signals is maintained when testosterone simultaneously promotes the development of elaborate signals and imposes an oxidative cost. Although there is evidence that testosterone enhances display traits in some cases, relatively few studies have tested the prediction that testosterone generates oxidative costs. We tested this prediction experimentally by administering testosterone (n = 14) and control (n = 14) implants to free-living common yellowthroat warblers (Geothlypis trichas) and quantifying testosterone and oxidative state before and 35 ± 15 days after implantation. We interpreted our experimental results in the context of a larger database of 83 unmanipulated males observed over five breeding seasons. In our observational data, testosterone was related to aspects of the carotenoid-based bib, but these relationships were age-dependent. Bib coloration was related to testosterone only for first time breeders, while bib size was positively and negatively associated with testosterone among experienced and inexperienced breeders, respectively. Two measures of oxidative metabolism—damage to DNA and total antioxidant capacity (TAC)—were unrelated to endogenous testosterone. Despite the correlation between endogenous testosterone and plumage, our experimental results failed to support the key prediction of the OHH. Testosterone treated males had higher levels of TAC upon recapture, but oxidative damage to DNA did not differ from controls. Because antioxidants can protect against the harmful effects of oxidative stress, one interpretation of our results is that males physiologically compensated for elevated testosterone, avoiding the honesty enforcing mechanism of the OHH. Taken together, our results suggest that testosterone is not a direct mediator of honest signaling in yellowthroats via its effects on oxidative stress.     

Screening the ability of rice roots to overcome the mechanical impedance of wax layers: importance of test conditions and measurement criteria

The development of a wax layer method for screening the ability of rice (Oryza sativa L.) roots to overcome mechanical impedance is described. Wax layers (3 mm thick) made of mixtures of white soft paraffin and paraffin wax were installed 50 mm deep in tubes of sand. The sand was watered with nutrient solution and planted with 3-d old rice seedlings. The numbers of root axes per plant that had penetrated the wax layers 24 d after planting were counted. The ratio of penetrated to total root axes per plant gave a misleading measure of root penetration ability, as rice varieties differed in the ratio of penetrated to total axes in a low impedance (3% wax) control. In non-flooded conditions, a 60% wax layer decreased root penetration (number of roots penetrating the wax layer per plant) to a mean of 74% of the low impedance control, whereas an 80% wax layer decreased mean root penetration to 31% of the control. The best measure of root penetration in non-flooded conditions was the number of axes penetrating an 80% wax layer. Flooding decreased root penetration of a 60% wax layer to a mean of 26% of the low impedance control. The best measure of root penetration in flooded conditions was the number of axes penetrating a 60% wax layer.     

An experimental test of diversity maintenance mechanisms,by a species removal experiment in a species-rich wooded meadow

Most theories of plant species coexistence assume the presence of diversity maintenance mechanisms, i.e. mechanisms enhancing species richness in a community. We wished to determine whether such a mechanism was operating by establishing a field experiment in the species-rich wooded meadow of Laelatu, western Estonia. Ten to seventeen subordinate species were removed periodically (for 4 years) from 10 permanent plots of 1×1 m (each plot had its specific list of excluded species; 10 plots served as control). Since the removed species were all subordinate ones, very little biomass was removed, but at the same time richness was reduced by 25–33%. If some diversity maintenance mechanism was operating, we would expect that immigration of other subordinate species would restore the original species richness. It was not possible to reject the null hypothesis of an identical immigration rate of new species into manipulated and control plots. The rate of small-scale species turnover was not affected by the removal of subordinate species. Interrelations of five richness characteristics were studied, by comparing empirical correlations among them, with those expected from a null model of random migration of species. The immigration rate of new species appeared to be related to the number of constant species, and immigration/extinction balance related to initial richness, more strongly than predicted by the null model. In the manipulated series these relationships matched the expectation from the null model. While the results generally support the so-called species pool hypothesis (and the carousel model), it seems that species small-scale turnover depends on the richness pattern in the studied grassland. In the case of plots with artificially reduced richness no departures can be detected from the random migration hypothesis.     

An experimental test of the efficiency of family selection in chickens

Summary Responses to single trait selection on individual phenotype and sire-family mean phenotype for survivor's egg weight and rate of lay were measured for a single generation in 13 replicates. Each replicate-selection criterion-trait subclass consisted of eight sire families or 72 females measured and was reproduced from the best 25% of the families or individuals. The realized heritability of egg weight was 0.39 and that of rate of lay was 0.31, both of which were significantly greater than zero but not significantly different from the predicted values based on halfsib correlations in the base population.The standardized response to sire-family selection was less than the response to individual selection for both traits and the difference was significant for rate of lay (0.10; 0.31) but not for egg weight (0.22; 0.39). The predicted responses to sire-family selection were less than those for individual selection for both traits, and the observed responses to sire-family selection were not significantly different from the predicted values for either trait.These experimental results do not disagree with the theoretical expectations of the relative efficiencies of individual and sire-family selection.Journal paper no. 7479, Purdue University, Agricultural Experiment Station. This investigation was conducted as a part of the cooperative research of the NC-89 Regional Poultry Breeding Project entitled Nature and Utilization of Genetic Variation in Poultry Improvement     

Protein folding: defining a "standard" set of experimental conditions and a preliminary kinetic data set of two-state proteins

Recent years have seen the publication of both empirical and theoretical relationships predicting the rates with which proteins fold. Our ability to test and refine these relationships has been limited, however, by a variety of difficulties associated with the comparison of folding and unfolding rates, thermodynamics, and structure across diverse sets of proteins. These difficulties include the wide, potentially confounding range of experimental conditions and methods employed to date and the difficulty of obtaining correct and complete sequence and structural details for the characterized constructs. The lack of a single approach to data analysis and error estimation, or even of a common set of units and reporting standards, further hinders comparative studies of folding. In an effort to overcome these problems, we define here a "consensus" set of experimental conditions (25 degrees C at pH 7.0, 50 mM buffer), data analysis methods, and data reporting standards that we hope will provide a benchmark for experimental studies. We take the first step in this initiative by describing the folding kinetics of 30 apparently two-state proteins or protein domains under the consensus conditions. The goal of our efforts is to set uniform standards for the experimental community and to initiate an accumulating, self-consistent data set that will aid ongoing efforts to understand the folding process.